The trick here is to use a large piece of graphic cardboard - that's the really thick cardboard that is NOT corrugated. That paper essentially behaves the same as sheet metal, so you can create a precise template for your transition panel. Once I got my template down and transferred to real metal, I simply clamped it everywhere then tacked into place, then riveted the ear flaps down to the bus.
I used the same template for both sides (flipped it over)
The cap was built into thirds - a left and right ear flap, and the center section. They are lapped so the center is "on top" of the left and right.
I do not possess the sheet metal shop punches, dies, large brake and other tooling to really do it "right" which in my opinion would be to have formed a flange to rivet below the low roof and high roof section.
Instead, the seam was done the way I have done other significant cab fabrication, just seam welding. If for some reason that section needed to be repaired, all the rivets could be drilled from the upper, lower, and transition section and lifted off as one huge roof panel section.
Here are two other revealing photos about it's construction. On the second photo, note the tape lines. In drafting parlance, the roof section is an off-plane extrusion of the curve representing the high side roof line. The tape just shows how the extrusion is in a single dimension.
Linear Mode
